My house was built in 1999, I have noticed very little water damage in the master bathroom. I am pretty sure it came from years of water being splashed out around the edges. I have already pulled the sheetrock around the tub surround and pulled it out a little bit to see if there was any damage underneath it but didnt see any and cant see any from the crawl space. The size of the damage is about 6"x8" and is in the corner of the tub and nearby wall and about a 2" hole that I pushed through to see how strong it was. I was wondering if I could just repair it from the crawl space underneath the house. I can get to the area easily. I was thinking about taking a small sheet of 3/4" plywood and place it between the joist and nail some supports between the joist to sandwich the plywood under the old subfloor and the 2x4's or 2x6's. Would be this be a acceptable repair or do I need to pull the tub/shower surround all the way out and repair it from the top. I am planning on tiling so it would be stronger after the backerboard and tile. Thanks guys!